Fine patterning of semiconductor integrated circuits has been achieved by progress in photolithography and its related technologies. As is well known, this photolithography is supported mainly by two technologies. One technology is related to the exposure light wavelength and numerical aperture of a miniaturized projection light exposure device called a stepper or a scanner, and the other is concerned with resist characteristics composed chiefly of transfer resolution of a photoresist composition onto which a mask pattern is to be transferred by the miniaturized projection light exposure device. By the combined actions of the two technologies, the processing accuracy of a semiconductor integrated circuit pattern by photolithography has been improved.
The wavelength of a light source used in the miniaturized projection light exposure device becomes shorter and shorter in accepting a demand for higher resolution of circuit patterns. Generally, g-line of 436 nm in a main spectrum of a mercury lamp is used for a resist resolution of about 0.5 μm; i-line of 365 nm in a main spectrum of the mercury lamp is used for a resolution of about 0.5 to 0.30 am; a KrF excimer laser light of 248 nm is used for a resolution of about 0.30 to 0.15 μm; an ArF excimer laser light of 193 nm is used for a resolution of about 0.15 μm or less; and use of an F2 excimer laser light of 157 nm, an Ar2 excimer laser light of 126 nm, and an EUV (extreme ultraviolet, wavelength 13 nm) light is examined for further fine patterning.
In view of the photoresist composition, on one hand, a combination thereof with an organic or inorganic anti-reflective coating film or a lighting system has been devised, and in lithography using a KrF excimer laser light, the life of a photoresist for KrF is prolonged, and a photoresist composition in consideration with about 110 nm of below λ/2 is under development. In lithography using an ArF excimer laser light, it is desired to provide photoresist compositions for ArF preferable for mass production in the future of those for a node of about 90 nm or less. Lithography using the F2 excimer laser attracts attention as technology taking responsibility for fine processing at 65 nm or less in the future, and a photoresist composition which can be applied satisfactorily to lithography using the F2 excimer laser is being developed.
As is well known in lithography, a photoresist layer applied on a laminate semiconductor substrate is irradiated with a short-wavelength light (light exposure) via a mask reflecting a negative or positive pattern of a semiconductor integrated circuit pattern to be realized. The photoresist composition contains, as a main component, a photosensitive polymer which upon reacting with the irradiation light, will be rendered insoluble (negative) or soluble (positive) with an alkali, and after exposure to the patterning light, is subjected to heat (post exposure bake, also referred to as “PEB”) for securing the reaction of the resist layer by light exposure, and then subjected to development to remove soluble parts, whereby a photoresist pattern layer accurately reflecting the circuit pattern to be realized is formed on the laminate semiconductor substrate. Thereafter, the patterned photoresist layer may be sufficiently cured by heating (post bake) to make it durable to etching in a next step. In the etching step, the surface layer or the top layer of the laminate semiconductor substrate is subjected to dry-etching along the pattern with the patterned photoresist layer as a mask.
Accordingly, the major properties required for the photoresist composition are to achieve resolution, and the first property for achieving this resolution is “transparency to irradiation light” by which the patterning irradiation light reaches not only the surface of the resist layer but also the bottom at the side of the substrate thereby sufficiently photosensitizing the irradiated portion as a whole in such thickness as to include the bottom. By securing this transparency, it is possible to realize a pattern of high resolution or an excellent pattern having a sectional shape in a rectangular shape having almost the same width from the top to base after patterning development.
To secure this transparency is also important for development of a resist composition coping with a shorter wavelength of irradiation light. For the transparency to exposure light, the development of a base polymer itself is advancing, and several kinds of excellent polymers have been proposed. As promising base polymers, fluorine-containing norbornene polymers (Non-patent document 1 (Proceedings of SPIE, Vol. 3999, (2000) pp357-364)), polymers in Patent document 1 (International publication WO 00/67072 Pamphlet) and Patent document 5 (Japanese Patent Application Laid-open No. 2002-333715), fluorine-containing monocyclic polymers (Patent document 2 (Japanese Patent Application Laid-open No. 2002-90997)), and polymers in Patent document 3 (International publication WO 02/64648 Pamphlet), Patent document 4 (International publication WO 02/65212 Pamphlet), and Non-patent document 2 (Shun-ichi Kodama, et al., “Synthesis of Novel Fluoropolymer for 157 nm Photoresists by Cyclo-polymerization” Proceedings of SPIE, Vol. 4690, (2000) pp76-83) have been reported.
These polymers, as can be confirmed or estimated from descriptions in these documents, are determined to be capable of securing transparency at the practical level to a light having a wavelength of 300 nm or less.